Perforated matrix character writing cathode ray display tube



ub w" June 30, 1964 F. A. RODGERS ETAL 3,139,574

PERFORATED MATRIX CHARACTER WRITING CATHODE RAY DISPLAY TUBE Filed A ril 1, 195a o w a \1 9' k I/ 9 INVENTORS k" CHARLES 1.. CORDERMAN FRANKLIN A. RODGERS AGENT United States Patent PERFQRATEB MATRDK CHARACTER WRITHJG CATHODE RAY DISPLAY TUBE Franklin A. Rodgers, Concord, and Charles L. Corderman, Winchester, Mass, assignors, by mesne assignments, to Massachusetts Institute of Technology, a corparation of Massachusetts Filed Apr. 1, 1958, Ser. No. 725,610

'7 Claims. ((1 313-86) This invention relates generally to cathode ray display tubes and more particularly to electron beam control thereof.

A cathode ray display tube is described in a co-pending application, Serial No. 509,471, filed by Franklin A.

' Rodgers on May 19, 1953, entitled, Cathode Ray Display Tube, now abandoned. The tube shown therein comprises a writing beam electron gun, two pairs of character selection plates, a thin metallic aperture-charactered matrix, an electron lens for focusing the character matrix on the target and for converging the beam back to the axis of the tube, two pairs of compensation plates for redirecting the beam parallel to the tube axis, and deflection means to position the beam upon the target. The writing beam produced by the electron gun is directed through the selection plates which direct the writing beam through one of the apertures in the character matrix which has the outline of a selected character. The beam is thus shaped corresponding to a desired character. The electron lens redirects the beam across the tube axis within the compensation plate pairs corresponding to the selection plate pairs. The compensation plates redirect the beam on and coaxial with the tube axis. The electron lens also serves to focus the desired character image at the matrix upon the target. Following repositioning of the electron beam by the electron lens and compensation plates on and coaxial with the tube axis, the deflection means deflects the beam to a selected elemental area on the target.

While representing a considerable advance over the prior art, the optics of the aforementioned application have limitations with regard to small character sizes and character intensity which make such display tubes unsuited for some applications.

It is, therefore, an object of this invention to provide improved electron beam control for a cathode ray display tube.

Another object of the invention is to provide an improved cathode ray display tube that permits the production of smaller symbol sizes at the target than have heretofore been possible.

Another object of the invention is to provide in a cathode ray display tube a substantial increase in symbol intensity as compared with existing devices.

Another object of the invention is to provide a cathode ray display tube having means to permit independent adjustment of the convergence and focusing functions.

Another object of the invention is to provide a cathode ray display tube which permits higher writing speeds than have heretofore been possible.

Another object of the invention is to provide a cathode ray display tube in which the electron beam undergoes smaller angular deviations than in existing devices.

Another object of the invention is to provide an improved cathode ray display tube which permits character sizes to be easily changed.

These and other objects of the invention are accomplished by a cathode ray display tube which is provided with an additional projection lens independent of the condensing lens and in which, in the preferred embodiment,

the character matrix is located at the optical center of the condensing lens.

The novel features which are believed to be characteristic of the invention both as to its organization and method of operation together with further objects and advantages thereof will be better understood from the follow ing description considered in connection with the accompanying drawings in which an embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of description only and are not intended as a definition of the limits of the invention.

FIGURE 1 is a diagrammatic view of a cathode ray display tube showing the electrical and mechanical relationships of the display tube components.

FIGURE 2 is a diagrammatic view showing the path of an envelope of all of the desired portions of the electron beams necessary to illuminate the matrix in the display tube.

Referring to FIGURE 1, an electron beam control system is shown for displaying any character such as, for example, a number or a letter. The control is employed in the evacuated envelope of a cathode ray display tube, the axis of which is indicated by 110. At the left extremity of the envelope 90, a Writing beam electron gun 10 is shown. In the direction of electron flow from the gun 10, there is shown character selection means 20 comprising a first pair of character selection plates 21 and a second pair of character selection plates 22 in orthogonal relationship to said first pair of selection plates 21.

The selection means 20 deflects the electron beam 106 to a predetermined aperture on the character matrix 40. The character matrix 40 consists of a thin metallic plate having apertures therein in the form of symbols such as letters or numbers which it is desired to display on the target. The character matrix 40 intercepts the undesired portions of the electron beam so that the beam 100 emerges having the cross-section of the desired symbol.

The character matrix 40 is positioned at the optical center of the condensing lens 30, hence this lens performs no focusing function on the configured beam. Condensing lens 30 serves to redirect the electron beam 100 across the axis within the compensation means 50. Compensation means 50 comprises vertical and horizontal pairs of compensation plates 51 and 52 respectively. The condensing lens serves to image the beam trajectory so that the vertical and horizontal paths of the trajectory cross the axis at the effective center of deflection of the corresponding vertical and horizontal compensation plate pairs 51 and 52. As the beam emerges from compensation means 50 its cross section is determined by the matrix character and it is coaxial with the electrical axis of the tube.

When magnetic condensing means 30 are used, the beam 100 will be rotated. For convenience in manufacture, the plates 51 and 52 of the compensation means 50 have been oriented 90 from the orientation of corresponding plates 21 and 22 of the selection means 20. This 90 rotation has been customary for compensation plates in the prior art. Unlike the prior art, however, the orientation of the character matrix 40 is no longer the same as, or nearly the same as, the orientation of the selection means 20. Since the character matrix 40 has been positioned at the optical center of the condensing means 30, one half of the total beam rotation between selection means 20 and compensation means 50 has occurred at the character matrix 40. Therefore, in the example of FIGURE 1, the orientation of the character matrix 40 is 45 from that of the selection means 20.

While the positioning of the character matrix 40 in the optical center of the condensing means 30 shown in FIGURE 1 is the preferred positioning, the matrix may l be positioned at any point between selection means and compensation means 50. Minimum tube length and minimum aberrations, however, are obtained with the positioning of matrix at the optical center of condensing means 30.

Projection lens serves to focus the image of the selected symbol at the character matrix 40 upon the target 31 Deflection means 70 following the projection lens serves to position the focused beam upon the desired area of target 80.

It will be noted that the electron beam control system of the invention differs from the aforementioned co-pending application in two major respects. First, the character matrix 40 is positioned within the condensing lens 30 rather than before lens 30. Second, a separate projection lens 60 is provided. In the co-pending application, the convergence lens serves both condensing and focusing functions.

The provision of independent means 30 and 60 for the convergence and projection focusing-functions provide several advantages over the prior art in which both functions were performed by a single means. Of particular importance, if the tube is to be used for recording or optical projection purposes, is the fact that less overall magnification of the characters can be obtained in a practical tube. This smaller character size on the face of the tube permits higher resolution and increases the density the prior art, the smaller character size with the same or 0 higher total beam current will mean that character brightness is increased. This increased brightness of characters is of particular value if the image is to be optically projected or recorded on media such as photographic emulsions. if increased brightness is not necessary in the particular'application, higher writing speeds may be utilized with the same character brightness as would have previously resulted at lower writing speeds. Another advantage which would become particularly noticeable if a display is projected to large sizes by optical means is the fact that the electron optics of this invention involve a pathillustrated in FIGURE 2-with smaller angular deviations from the axis of the tube for the same magnetic field strengths. The deviations in FIGURE 2 have been exaggerated for the sake of clarity in the drawing. The decrease in angular deviation results in a corresponding decrease in the distortion introduced into individual characters. Alternatively, if the same degree of distortion is to be tolerated, the tube length can be shortened through the use of increased field strengths.

Not only do the electron optics of this invention permit superior operating characteristics as noted above, but also this improvement is achieved in a structure which is simpler to produce and adjust in use. In the prior art condensing and focusing were accomplished by a single means, so that it was impossible to adjust one characteristic without a corresponding change being introduced into the other characteristic. The provision of independent means 30 and 60 in the optics of this invention enables independent adjustments to be made, each adjustment having substantially no effect upon the other characteristic. Furthermore, it is even possible to change the displayed character size in a completed tube by simply changing the positioning of the projection focusing means 6%. If one attempts to change the display character size in the prior art display tubes, the condensing characteristics are also changed so that the beam is no longer properly positioned with respect to the compensation plates. Thus, as a practical matter it has not previously been possible to change the size of the displayed characters once a given tube design has been adopted.

While the embodiment of FIGURE 1 utilizes magnetic convergence and projection focusing means, it will be obvious to one skilled in the art that any appropriate method of focusing an electron beam such as by means of electrostatic focusing rings may be used. Similarly, although electrostatic deflection means are shown, magnetic means could also be used. Likewise, the optics are equally suitable for use in cathode ray tubes of the storage type wherein means are provided to retain the displayed characters. Although the embodiment of FIGURE 1 has means for horizontal and vertical positioning upon the target area, such positioning may be unnecessary in some applications. In some instances only one coordinate may be required, as for the the horizontal recording of data upon a moving recording medium. Hence, it is to be understood that the above-described examples are merely illustrative and modifications may be made therein without departing from the meaning and range of equivalents of the following claims.

What is claimed is:

1. A cathode ray tube comprising a target area, deflection means disposed along the axis of said tube and adapted to act upon an electron beam, condensing means disposed after said deflection means for directing said beam back toward said tube axis after said beam has been deflected away from said axis by said deflection means, said condensing means performing substantially no projection focusing function, compensation means disposed after said condensing means for directing said beam along said tube axis after said beam has been directed toward said axis by said condensing means, and projection focusing means disposed after said compensation means for focusing said beam upon said target area, said projection focusing means performing substantially no condensing function.

2. A cathode ray tube comprising a target area, first and second deflection systems disposed along the axis of said tube and adapted to successively act upon an electron beam, condensing means disposed between said deflection systems for directing said beam back toward said tube axis after said beam has been deflected away from said axis by said first deflection system said condensing means performing substantially no projection focusing function, compensation means disposed between said condensing means and said second deflection system for directing said beam along said tube axis after said beam has been directed toward said axis by said condensing means and projection focusing means disposed between said compensation means and said second deflection system for focusing said beam upon said target area, said projection focusing means performing substantially no condensing function.

3. A cathode ray tube comprising a target area, first and second deflection systems disposed along the axis of said tube and adapted to successively act upon an electron beam, compensation means adapted to act upon said electron beam, a character matrix, said first deflection means deflecting said electron beam through a predetermined portion of said character matrix, condensing means centered about said matrix for redirecting said beam back to said tube axis at said compensation means, said condensing means performing substantially no projection focusing function, said compensation means serving to redirect said beam coaxial with said tube axis and projection focusing means disposed between said compensation means and said second deflection systems for focusing said beam on said target area, said projection focusing means performing substantially no condensing function.

4. A cathode ray tube comprising a target area, first and second deflection systems disposed along the axis of said tube and adapted to successively act upon an electron beam, compensation means adapted to act upon said electron beam, a character matrix, said character matrix having a plurality of character shaping portions disposed in a two dimensional array, said first deflection means deflecting said electron beam through a predetermined portion of said character matrix, magnetic condensing means centered about said matrix for redirecting said beam back to said tube axis at said compensation means, said condensing means performing substantially no projection focusing function, the two dimensional array of said matrix being disposed about said tube axis at an angle equal to the amount of rotation imparted to said beam by said condensing means, said compensation means serving to redirect said beam coaxial with said tube axis, and projection focusing means disposed between said compensation means and said second deflection system for focusing said beam on said target area, said projection focusing means performing substantially no condensing function.

5. A cathode ray tube comprising a target area, first and second deflection systems disposed along the axis of said tube and adapted to successively act upon an electron beam, compensation means adapted to act upon said electron beam, a character matrix, said first deflection means comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair, said first deflection means deflecting said electron beam through a predetermined portion of said character matrix, condensing means centered about said matrix for redirecting said beam back to said tube axis at said compensation means, said condensing means performing substantially no projection focusing function, said compensation means comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair, the said compensation means serving to redirect said beam coaxial with said tube axis and projection focusing means disposed between said compensation means and said second deflection system for focusing said beam on said target area, said projection focusing means performing substantially no condensing function, said second deflection system comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair, said second deflection means serving to direct said beam to a predetermined position on said target area.

6. A cathode ray tube comprising a target area, first and second deflection systems disposed along the axis of said tube and adapted to successively act upon an electron beam, compensation means adapted to act upon said electron beam, a character matrix, said character matrix having a plurality of character cutout portions for selectively altering the cross sectional shape of the beam in accordance with one of said portions of the beam-shaping member through which the electron beam is projected, said member having its character cutout portions disposed in a two dimensional array, said first deflection means comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair, said first deflection means deflecting said electron beam through a predetermined portion of said character matrix, condensing means comprising a coil centered about said matrix, said condensing means performing substantially no projection focusing function, the two dimensional array of said matrix being disposed about said tube axis at an angle with respect to that of said first deflecting elements equal to the amount of rotation imparted to the beam by said coil said condensing means serving to redirect said beam back to said tube axis at said compensation means, said compensation means comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair, the two pairs of deflecting elements being disposed about the path of the beam at an angle with respect to that of said first deflecting elements equal to the amount of rotation imparted to said beam by said condensing coil, the said compensation means serving to redirect said beam coaxial with said tube axis and projection focusing means disposed between said compensation means and said second deflection system for focusing said beam on said target area, said projection focusing means performing substantially no condensing function, said second deflection ,system comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair said second deflection means serving to direct said beam to a predetermined position on said target area.

7. In an evacuated container having a target at one end and a source of electrons at the other end for projecting a beam of electrons toward the target substantially along a longitudinal axis of said container, a beam-shaping member having a plurality of character cutout portions for selectively altering the cross sectional shape of the beam in accordance with one of said portions of the beamshaping member through which the electron beam is projected, said member having its character cutout portions disposed in a two dimensional array, a first deflection means comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair, condensing means having an electrical axis substantially coaxial with the longitudinal axis of the container, said condensing means performing substantially no projection focussing function, said condensing means being centered about said beam-shaping member and substantially redirecting and converging the beam to the longitudinal axis, second deflection means comprising two pairs of deflecting elements, the deflecting elements of one pair being crossed relative to and axially spaced from the elements of the other pair, said second deflection means referencing the beam to a position coaxial with said longitudinal axis of the container, projection focusing means disposed after said second deflecting means for focusing said beam upon said target, said projection focusing means performing substantially no condensing function, and third deflection means encompassing the axially referenced beam for deflecting the beam toward predetermined locations on the target, the condensing means and the elements of the first and second deflecting means being axially disposed relative to one another wherein one pair of elements of the first deflection means is focused by the condensing means into the respective pair of elements of the second deflection means, and the second pair of elements of the first deflection means likewise is focused by the condensing means into the second pair of elements of the second deflection means.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A CATHODE RAY TUBE COMPRISING A TARGET AREA, DEFLECTION MEANS DISPOSED ALONG THE AXIS OF SAID TUBE AND ADAPTED TO ACT UPON AN ELECTRON BEAM, CONDENSING MEANS DISPOSED AFTER SAID DEFLECTION MEANS FOR DIRECTING SAID BEAM BACK TOWARD SAID TUBE AXIS AFTER SAID BEAM HAS BEEN DEFLECTED AWAY FROM SAID AXIS BY SAID DEFLECTION MEANS, SAID CONDENSING MEANS PERFORMING SUBSTANTIALLY NO PROJECTION FOCUSING FUNCTION, COMPENSATION MEANS DISPOSED 